Dibenzothiophene S, S-Dioxide-Containing Dipolar Molecules As Efficient Hole-Transport Materials for p-i-n Perovskite Solar Cells

Organic-inorganic hybrid perovskite solar cells (OIH-PSCs) have developed rapidly in the past decade, and the commercialization of OIH-PSCs demands low-cost hole-transport materials (HTMs) with high performance and stability. The present study synthesized two organic HTMs containing dibenzothiophene S-dioxide as the acceptor unit and triphenylamine as the donor (denoted by TPAF-SO2 and TPA-SO2). In TPAF-SO₂, the methoxy group and adjacent fluorine atom were introduced to decrease the highest occupied molecular orbital energy level. In TPA-SO₂, the methyl sulfide group is the end group that can passivate the lead ion. TPAF-SO₂ and TPA-SO₂ exhibit hole-transport mobilities as high as 1.12 × 10^-3 and 2.31 × 10^-3 cm² v^-1 s^-1, respectively, and strongly passivate Pb vacancies. Compared with TPAF-SO₂, TPA-SO₂ is more suitable for the growth of perovskite crystals. The perovskite grown on the latter has a lower trap density and higher carrier mobility; thus, both the nonradiative recombination and the charge-transport loss are decreased. The OIH-PSC based on TPA-SO₂ as the HTM achieved a power conversion efficiency (PCE) as high as 22.08%, whereas the device based on TPAF-SO₂ achieved a PCE of only 18.42%. In addition, the unencapsulated device based on TPA-SO₂ can maintain 85% of the initial PCE after being stored in N₂ for 1200 h, whereas the device based on TPAF-SO₂ decayed rapidly to zero in 800 h under the same conditions.